Arsenic adsorbing composition and methods of use

ABSTRACT

In various embodiments, the present disclosure provides filtering compositions, their method of production, and methods for their use. In specific implementations, the filtering composition includes lanthanum and has a surface area of at least about 125 g/m 2 . In more specific examples, the filtering composition is free-flowing or has a moisture content between about 10 wt % about 30 wt %. Particular compositions include at least one of iron or magnesium. Some embodiments of the present disclosure provide filtering compositions that are resilient or leach-resistant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/735,969, filed Apr. 16, 2007, entitled “ARSENIC ADSORBING COMPOSITIONAND METHODS OF USE,” the disclosure of which is hereby incorporated byreference, which is now U.S. Pat. No. 8,110,526. U.S. patent applicationSer. No. 11/735,969 claims the benefit of, and incorporates byreference, U.S. Provisional Patent Application No. 60/792,233, filedApr. 14, 2006.

TECHNICAL FIELD

The present disclosure relates generally to compositions and methods forpurifying solutions. In specific implementations, the present disclosureprovides compositions for removing anions, such as arsenic anions, fromsolutions.

BACKGROUND

Arsenic is a naturally occurring element in the earth's curst and can befound in many natural ecosystems. Mining of arsenic containing oresoften releases arsenic into the soil. Burning of arsenic containingfossil fuels, volcanic eruptions, and weathering processes also canintroduce substantial amounts of arsenic into the environment. Variousindustrial activities such as smelting, petroleum refining, pesticideand herbicide manufacturing, and glass and ceramic production cangenerate arsenic containing wastewater. The presence of arsenic innatural waters may originate from geochemical reactions, industrialwaste discharges or agricultural use of pesticides containing arsenic.Arsenic is typically mobile within the environment and may circulatemany times in various forms through the atmosphere, water, and soilbefore finally entering into sediments.

Hyper-pigmentation, skin cancer, liver cancer, circulatory disorders,and other ailments have been attributed to the presence of arsenic inwater. The United States Environmental Protection Agency (USEPA) hasidentified arsenic as a group “A” known carcinogen. This classificationis based on sufficient evidence of carcinogenicity from human datainvolving occupational and drinking water exposures. Arsenic presents apotential health problem due to its toxicity. In response to thesehealth concerns, the USEPA, in January 2001, promulgated the new arsenicrule that lowered the maximum contaminant level (MCL) in drinking waterto 10 μg/L (10 ppb) for both community and non-transient, non communitywater systems. Previously, the Safe Drinking Water Act (SDWA) had aminimum arsenic standard of 50 ppb. The USEPA lowered the standard basedon recommendations by the National Research Council, which reviewedscientific studies on the health effects of arsenic on humanpopulations. According to some estimates, conventional water treatmentsystems will cost the nation between $180 and $725 million to meet the10 ppb standard set by the USEPA.

Arsenic Chemistry

Arsenic often occurs in inorganic form in aquatic environments, oftenresulting from the dissolution of solid phases such as arsenolite(As₂O₃), arsenic anhydride (As₂O₅) and realgar (AsS₂). The chemistry ofarsenic in aquatic systems is typically complex because the element canbe stable in four major oxidation states (+5, +3, 0 and −3) underdifferent redox conditions. In natural waters arsenic is typically foundas an anion with acid characteristics in only the As (III) and As (V)oxidation states. In oxygenated waters, the oxyanions of arsenictypically exist in four different arsenate species as H₃AsO₄, H₂A_(S)O₄² and A_(S)O₄ ³ in the pH ranges of <2, 3-6, 8-10 and >12, respectively.Arsenite is more likely to be found in oxygen free (anaerobic)groundwater, while arsenate is more common in aerobic surface water.Arsenite ions are typically oxidized to arsenate in the presence ofoxygen, chlorine, or potassium permanganate. Therefore under neutralconditions and acidic conditions, As (III) exists as a neutral speciesand cannot be adsorbed by an adsorbent based on ionic interaction alone.The chemistry of arsenic is more fully described in U.S. Pat. No.6,197,201.

Several methods for reducing arsenic concentrations to acceptable levelshave been studied and are in current use. These methods includecoagulation and precipitation using ferric chloride and sulfate, ionexchange, reverse osmosis, and adsorption using activated carbon andalumina. These methods are effective to a certain extent. However, thesemethods can be considerably more expensive, and generally narrower inapplication, than is typically desired for the treatment of largevolumes of water. In addition, it can be difficult to implement smallerscale filtration using existing filtering techniques, such as incolumns. These difficulties can make it difficult to implementpoint-of-use or point-of-entry filtration.

The use of ferric chloride, hydrated lime, sodium sulfate and alum tocoagulate water-containing arsenic has been described. Harper et al.,“Removal of Arsenic from Wastewater using Chemical PrecipitationMethods”, 64(3) Water Environment Research 200-203, 1992. These methodstypically require multiple treatments of water with coagulationchemicals, and large amounts of chemicals relative to the amount ofarsenic present, to obtain the desired reduction in arsenicconcentration. In addition, the methods typically produce sludge thatrequires dewatering or solidification and eventually storage in alandfill as hazardous waste. Also, the ferric chloride process typicallyrequires a pH of less than 6.5. Merrill et al., “Field Evaluation ofArsenic and Selenium by Iron Co-precipitation”, “6(2) EnvironmentalProgress 82-90, 1987.

A method of precipitating arsenite and arsenate ions from aqueoussolutions using yttrium carbonate at alkaline pH has also beendescribed. Wasay et al. “Removal of Arsenite and Arsenate Ions fromAqueous Solution by Basic Yttrium Carbonate”, 30(5) Wat. Res. 1143-1148,1996. This method typically requires strict control of pH to achievearsenic removal sufficient to comply with environmental standards. Inaddition, the effective pH range was found to depend on which arsenicspecies was desired to be precipitated.

U.S. Pat. No. 3,956,118 purports to disclose a process for removingphosphate ions from wastewater using a rare earth salt. However, thedisclosed process appears to be limited to removal of phosphates.

Adsorbents, such as lanthanum oxide and lanthanum-alumina oxide, havebeen used for removing arsenate and arsenite species from solution, suchas described in U.S. Pat. No. 5,603,838. This patent purports todisclose that lanthanum oxide alone, or in conjunction with aluminasolids and other oxides, can remove arsenic to low levels (<50 ppb). Theadsorption kinetics were stated to be extremely fast compared to otheradsorbents such as alumina. Davis et al., “Transport Model for theAdsorption of Oxyanions of Selenium (IV) and Arsenic (V) from water ontoLanthanum and Alumina Oxide”, Journal of Colloid and Interface Science,188, 1997, p. 340-350; Misra et al. “Adsorption of Oxyanions of Seleniumonto Lanthanum Oxide and Alumina”, Minor Elements 2000, Published bySME, February 2000, pp. 345-353; Misra et al., “Adsorption andSeparation of Arsenic from Process Water Using LS™ (Lanthanum-SilicaCompound)”, Proceedings of the Randol Gold Forum'97, 1997, pp. 203-206;Rawat et al., “Adsorption of the Oxyanions of Arsenic onto LanthanumOxide”, EPD Congress, The Minerals, Metal and Materials Society (TMS),Warrendale, Pa., 1998, pp. 14-23.

A novel precipitation process developed by Misra et al. (U.S. Pat. No.6,197,201) uses lanthanum chloride and optionally other salts toselectively co-precipitate arsenite and arsenate from process water.Misra et al., “Enhanced Precipitation and Stabilization of Arsenic fromGold Cyanidation Process”, Minor Elements 2000, Published by SME,February 2000, pp. 141-148; Nanor et al., “Removal and Stabilization ofArsenic”, Randol Gold Forum, 1999, pg. 191-196; Nanor et al., 1998. U.S.Patent Publication No. 2006/0086670 to Misra et al., describes the useof lanthanum hydroxide compositions to precipitate and remove arsenicfrom solutions.

General drawbacks of the processes discussed above can includeinefficient removal of arsenic to an acceptably low level for drinkingwater and discharge into ground water, the problem of filtration ofprecipitated sludge, and fouling of resins and membranes. In addition,once the arsenic species are removed, the solid materials formed musttypically be disposed of. The solid materials formed from the aboveprocesses also can be susceptible to leaching of the metals at a futuretime. Although the pre-coat process can remove arsenic from drinkingwater to below 10 ppb, it typically requires about 10 minutes of contacttime to accomplish this. In addition, precipitate build up on thesurface of the bed can reduce flow rates and require frequent cleaningor replacement of the bed.

Problems involving transportation, storage, and use of prior filteringcompositions can also be encountered. For example, compositions whichare maintained in a wet or highly moist state can be difficult totransport or to pack into a column or bed for use.

SUMMARY

Particular embodiments of the present disclosure provide filteringcompositions having a comparatively high surface area. In someimplementations, the filtering compositions are dry, free-flowingmaterials. In specific examples, the filtering compositions have amoisture content between about 10% and about 30%. Particular disclosedcompositions have a crystalline structure, while other disclosedcompositions have an amorphous structure. In specific examples, thecompositions are resilient or leach resistant.

In further implementations, the filtering compositions have a surfacearea of at least about 125 m²/g, such as about 125 m²/g to about 350m²/g, such as about 150 m²/g to about 250 m²/g. In specific examples,the filtering compositions have a surface area of at least about 175m²/g, such as about 175 m²/g to about 200 m²/g. In further examples, thefiltering compositions have a surface area of at least about 200 m²/g.In yet further implementations, the compositions have a density betweenabout 0.5 g/cc and 1.2 g/cc, such as between about 0.6 g/cc and about1.0 g/cc.

Particular compositions of the present disclosure include a mixture oflanthanum and at least one other element. In specific examples, thecomposition includes a mixture of lanthanum and iron or a mixture oflanthanum, iron, and magnesium. In some implementations when lanthanumand iron are used, the molar ratio of iron to lanthanum is about 4:1 toabout 1:2, such as about 2:1 to about 1:0. In a specific example, theiron to lanthanum ratio is about 1:1. In some examples where thecompositions contain lanthanum-iron-magnesium, the molar ratio may beabout 10:1:1 to about 50:5:1. In further examples, thelanthanum-iron-magnesium ratio is about 1:2:0.05 molar. The compositionsare formed, in some examples, by precipitation from a salt solution ofthe active agents. In a particular example, at least one of the salts isa nitrate salts. In a more particular example, all of the metal saltsare supplied as nitrate salts.

In accordance with other embodiments of the present disclosure, theabove mixture is combined with a substrate. The substrate, in particularexamples, is diatomaceous earth, such as calcined diatomaceous earth. Insome implementations, the composition contains up to about 30 percent byweight active agent. Lanthanum and the other elements may be initiallyprovided to the substrate in a variety of forms, such as a solution of asalt of the element. In a particular example, the nitrate salts areused.

Particular embodiments of the present disclosure provide resilient orleach-resistant filtering compositions. Certain compositions have a zetapoint of at least about pH 9.0, such as in the range of about pH 9.0 toabout pH 10.0, such as between about pH 9.5 to about pH 9.8. Higher zetapoints can indicate more resilient or leach resistant compositions.

The present disclosure also provides method for forming filteringcompositions. According to a disclosed method, a solution of activeagent is added to a precipitating solution. The active agent solution,in more particular examples, is a salt solution of the active agent oragents (or their precursors), such as an acidic salt solution. Theprecipitating solution may be a basic solution, such as a sodiumhydroxide solution. In particular methods, the rate of addition of theactive agent solution is controlled such that the temperature of themixed solution does not exceed a predetermined threshold temperature ortemperature change. In particular examples, the temperate of the mixedsolution is kept between below about 60° C., such as below about 45° C.In a specific example, the temperature is maintained between about 35°C. and about 45° C. In other embodiments, the basic solution is added tothe active agent solution. One or both of the solutions may include asupport material.

In yet further embodiments, filtering compositions are prepared byadding the active agent in solid form to a support. In particularexamples, the active agent includes at least one of lanthanum hydroxide,lanthanum-iron hydroxide, or lanthanum-iron-magnesium. In yet furtherembodiments, the active agent is selected from nanocrystals oflanthanum, lanthanum oxy-hydroxide, and/or lanthanum on iron materials,such as lanthanum-ferric oxy-hydroxide and lanthanum-ferric-magnesiumoxy-hydroxide.

In conjunction with precipitation of an active agent solution, oraddition of a precipitated active agent to a support, mixing can beapplied. In some cases, mixing is applied for an additional period oftime after the addition is complete, such as an additional 2 hours. Inparticular examples, agitation is carried out using a standardcommercial mixing apparatus operating at about 200 rpm to about 500 rpm,such as about 300 rpm.

In further embodiments, the method of making the filtering compositionincludes drying the composition formed from mixing the active agent andsubstrate. In a particular implementation, the composition is drieduntil it has a water content of about 10% to about 30%. In moreparticular implementations, the drying process is carried out atrelatively low temperatures, such as less than about 200° C., such asbetween about 60° C. and about 100° C. In particular examples, thedrying time is about 12 to about 36 hours, such as about 16 to about 24hours.

In particular methods of the present disclosure, ultrasonication isapplied to the composition after and/or during precipitation of theactive agent or addition of the active agent to a support. In particularmethods, the composition is ultrasonicated after mixing for a period ofabout 10 to about 60 minutes at a frequency of about 25 kHz to about 42kHz. In some implementations, ultrasonication can provide more resilientor leach-resistant compositions.

The present disclosure also provides methods of using the disclosedfiltering agents. In particular methods, the filtering agent is placedin a quantity of liquid and added to a column or bed. A solutioncontaining the material to be removed is passes through the column orbed of material and at least a portion of a solute is retained by thefiltering composition. In particular examples, the solute is arsenic. Infurther examples, the solute is one or more of arsenic, tungsten,fluoride, boron, vanadium, phosphate, or bicarbonate.

Particular compositions are suitable for use inpoint-of-entry/point-of-use systems, such as having suitably fastadsorption kinetics and are able to adsorb a sufficient amount ofmaterial to provide a useful system life.

There are additional features and advantages of the subject matterdescribed herein. They will become apparent as this specificationproceeds.

In this regard, it is to be understood that this is a brief summary ofvarying aspects of the subject matter described herein. The variousfeatures described in this section and below for various embodiments maybe used in combination or separately. Any particular embodiment need notprovide all features noted above, nor solve all problems or address allissues in the prior art noted above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are shown and described in connection with thefollowing drawings in which:

FIG. 1 is a scanning electron micrograph of a disclosed lanthanumhydroxide material.

FIG. 2 is a scanning electron micrograph of a disclosedlanthanum-iron-magnesium hydroxide material.

FIG. 3 is a graph showing the effects of temperature and amount of adisclosed LaH filtering composition on arsenic removal.

FIG. 4 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition.

FIG. 5 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron-magnesium (32-100 mesh)filtering composition.

FIG. 6 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed LaH (32-100 mesh) filtering composition.

FIG. 7 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed LaH (100-270 mesh) filtering composition.

FIG. 8 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron-magnesium filtering (100-270mesh) composition.

FIG. 9 is a graph of lanthanum concentration versus bed volumes ofsolution of a disclosed LaH (32-100 mesh) filtering composition.

FIG. 10 is a graph of lanthanum concentration versus bed volumes ofsolution of a disclosed lanthanum-iron-magnesium (32-100 mesh) filteringcomposition.

FIG. 11 is a graph of lanthanum concentration versus bed volumes ofsolution of a disclosed lanthanum-iron-magnesium (100-270 mesh)filtering composition.

FIG. 12 is a graph of lanthanum concentration versus bed volumes ofsolution of a disclosed LaH (100-270 mesh) filtering composition.

FIG. 13 is a flowchart illustrating a method of making a disclosedlanthanum-iron filtering composition.

FIG. 14 is a flowchart illustrating a method of making a disclosedlanthanum-iron filtering composition.

FIG. 15 is a flowchart illustrating a method of making a disclosedlanthanum-iron filtering composition.

FIG. 16 is a flowchart illustrating a method of making a disclosedlanthanum-iron filtering composition.

FIG. 17 is a graph of arsenic concentration versus bed volumes ofsolution for disclosed lanthanum-iron filtering compositions A and B.

FIG. 18 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron filtering compositions C and D.

FIG. 19 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition E.

FIG. 20 is a graph of arsenic concentration versus bed volumes ofsolution for disclosed lanthanum-iron filtering compositions F, G, andH.

FIG. 21 is a graph of arsenic concentration versus bed volumes ofsolution for a spent lanthanum-iron filtering composition I.

FIG. 22 is a graph of iron concentration versus bed volumes of solutionfor a spent lanthanum-iron filtering composition I using alkaline andacidic media.

FIG. 23 is a graph of lanthanum concentration versus bed volumes ofsolution for a spent lanthanum-iron filtering composition I in alkalineand acidic media.

FIG. 24 is a graph of zeta potential versus pH for a filteringcomposition I, Fe₂O₃, and Fe(OH)₃

FIG. 25 is a graph of arsenic concentration versus time for a disclosedfiltering composition I and a commercially available iron hydroxidematerial at pH 4.0.

FIG. 26 is a graph of arsenic concentration versus time for a disclosedfiltering composition I and a commercially available iron hydroxidematerial at pH 9.0.

FIG. 27 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I, alanthanum hydroxide composition J, and a commercially available ironhydroxide material.

FIG. 28 is graph of arsenic concentration versus bed volumes of solutionfor a disclosed lanthanum-iron filtering composition I at various pHs.

FIG. 29 is graph of arsenic concentration versus bed volumes of solutionfor a disclosed lanthanum-iron filtering composition I and acommercially available iron hydroxide material.

FIG. 30 is a graph of arsenic concentration versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I and acommercially available iron hydroxide material.

FIG. 31 is a graph of percent anion removal versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I.

FIG. 32 is a graph of percent anion removal versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I atvarious pH.

FIG. 33 is a graph of percent anion removal versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I and acommercially available composition at pH 6.0-6.6.

FIG. 34 is a graph of percent anion removal versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I at pH6.5.

FIG. 35 is a graph of percent anion removal versus bed volumes ofsolution for a disclosed lanthanum-iron filtering composition I at pH8.5.

DETAILED DESCRIPTION

Unless otherwise explained, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this disclosure belongs. In case of any suchconflict, or a conflict between the present disclosure and any documentreferred to herein, the present specification, including explanations ofterms, will control. The singular terms “a,” “an,” and “the” includeplural referents unless context clearly indicates otherwise. Similarly,the word “or” is intended to include “and” unless the context clearlyindicates otherwise. The term “comprising” means “including;” hence,“comprising A or B” means including A or B, as well as A and B together.All numerical ranges given herein include all values, including endvalues (unless specifically excluded) and intermediate ranges.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present disclosure,suitable methods and materials are described herein. The disclosedmaterials, methods, and examples are illustrative only and not intendedto be limiting.

As used herein, “removing” means the concentration of one or moresubstances in a solution is reduced to a desired level. For example,“removing arsenic from arsenic-containing water” means reducing theconcentration of arsenic, such as in the form of arsenite and arsenate,in arsenic-containing water to a desired level, such as to aconcentration below about 10 ppb, such as below about 5 ppb.

“Arsenic-containing water” may contain elements in addition to arsenic.

“Aqueous solution” refers to a solution in which water is a dissolvingmedium or solvent. The pH of the aqueous solution may be adjusted by anymeans known by those of ordinary skill in the art, including by theaddition of magnesium oxide, calcium hydroxide, and/or sodium hydroxideto raise the pH, and the addition of hydrochloric acid or otherinorganic acids to lower the pH.

“Adsorbent,” “adsorbing composition,” or “filtering composition” referto a material that physically or chemically removes one or moresubstances of interest, such as ions, from a solution, such as anaqueous solution. “Active agent” refers to one or more materials in anadsorbing composition which actively remove the substances from solutionwhile “substrate” or “support” refers to a comparatively inert material,or a mixture of such materials, on which the active agent is disposed orwith which the active agent is mixed. Certain of the disclosedcompositions include only active agents while others include both activeagents and a support. In particular examples, the active agent isprepared from a metal salt, such as a nitrate salt, sulfate, carbonate,or chloride salt.

“Solid materials,” such as those formed from the action of an adsorbent,include amorphous materials and crystalline materials or mixtures.

“Lanthanum chloride” refers to both pure and impure lanthanum chloride.Impure lanthanum chloride can contain various elements of the lanthanideseries in addition to lanthanum. The lanthanide series of elementsincludes the elements lanthanum, cerium, praseodymium, and neodymium.

Certain active agents disclosed herein are “metal salt hydroxides,”hydroxides formed from one or more metal salts. Metal salt hydroxidescan be added already in the hydroxide form or can be converted to thehydroxide form, such as by precipitation from a salt solution using abase, lime, or magnesium oxide, as known in the art. Suitable saltsuseable to prepare metal hydroxides include nitrate, sulfate, chloride,and carbonate salts.

As used herein, “contacting” means placing two or more substances, suchas arsenic-containing water and a filtering composition, together sothat a desired reaction occurs to a desired extent.

“Resilient,” as used herein, means that a filtering composition resistsbeing broken down into smaller particles. For example, nanocrystallinecompositions may be more resilient than amorphous compositions otherwisehaving similar properties or chemical composition. The presentdisclosure provides methods for making such resilient compositions.Resilient compositions may provide other benefits, such as resistingleaching of absorbed materials.

“Leach resistant,” as used herein, refers to a material being resistantto chemical or physical removal of absorbed species as compared withanother material. For example, for adsorbent compositions, a material isconsidered “leach resistant” with respect to another material if itloses less of an absorbed material, such as arsenic ions, overequivalent periods of time or exposure, such as during passage of aliquid through the material or storage of the material, such as in alandfill. Leach resistant can also mean that a composition satisfies aparticular test or meets or exceeds a particular standard.

In specific examples, leach resistance can be correlated with the zetapotential and zeta point of a composition. For example, in arsenicabsorption applications, the zeta point, or point at which thecomposition has a zero zeta potential, can indicate the point at whicharsenic is no longer absorbed. Particular disclosed compositions have azeta point of at least about pH 9.0, such as in the range of about pH9.0 to about pH 10.0. In specific examples, the compositions have a zetapoint in the range of about pH 9.5 to about pH 9.8.

In particular embodiments, the present disclosure provides filteringcompositions which include lanthanum hydroxide. The lanthanum used toproduce disclosed filtering compositions can be pure or can be mixedwith other elements of the lanthanide series. Lanthanum hydroxide canalso be used in combination with other metals such as ferric hydroxide,ferric nitrate, magnesium hydroxide, magnesium oxide, and magnesiumnitrate. Certain embodiments combine magnesium oxide, iron chloride andlanthanum chloride at various ratios, which, under certain disclosedconditions, form nanocrystalline oxy-hydroxide media. Furtherembodiments combine lanthanum nitrate and ferric nitrate at variousratios. Yet further embodiments combine lanthanum carbonate and ironpowder at various ratios, including in the presence of nitric acid, inparticular implementations.

The lanthanum containing compositions are mixed with a support material.Suitable supports for the disclosed filtering compositions form porousstructures and adsorb the disclosed active agents. Suitable supportsinclude diatomaceous earth, including calcined diatomaceous earth,cellulose, and perlite, and mixtures thereof. In particular examples,the support has a size of between about 20 and about 270 mesh, such asbetween about 30 and about 60 mesh. Suitable support materials areavailable from EP Minerals, LLC, of Reno, Nev.

In particular implementations, the active agent includes a mixture oflanthanum and at least one other element, such as iron or magnesium.Suitable lanthanum and iron sources include salts of the metals, such aschloride, sulfate, carbonate, or nitrate salts. In specific examples,the active agent has a molar ratio of iron to lanthanum of about 4:1 toabout 1:2, such as from about 2:1. In a specific example, the activeagent has a lanthanum to iron ratio of at least about 10:1. In morespecific examples, the ratio of iron to lanthanum is about 1:1. Furtherexamples include both iron and magnesium, such as from a magnesium oxidesource, such as in a molar ratio of lanthanum-iron-magnesium of about10:1:0.1 to about 50:5:0.05. In further embodiments, the molar ratio maybe from about 1:1:0.9 to about 1:4:0.1 iron to lanthanum to magnesium.In a more particular example, the molar ratio is about 1:1.5:0.1iron:lanthanum:magnesium.

For the removal of arsenic ions, in particular embodiments, a lanthanumhydroxide media includes from about 10 to about 5000 moles of lanthanumfor every mole of arsenic ions in solution. Lanthanum-iron-magnesiumcompositions typically have about 10 to about 5000 moles of lanthanum,about 1 mole to about 500 moles iron, and about 1 to about 100 moles ofmagnesium for each mole of arsenic ions in a solution to be filtered.

The present disclosure provides compositions have a comparatively highsurface area and methods for their production. For example, disclosedcompositions can be produced with a surface area of about 125 m²/g toabout 350 m²/g, such as about 150 m²/g to about 250 m² g. In morespecific examples, the compositions have a surface area of about 175m²/g to about 200 m²/g. Compositions having higher surface areas canallow the compositions to absorb materials more quickly or absorb agreater amount of material compared with materials with lower surfaceareas.

In particular embodiments, the density of the disclosed compositionprovides desired physical properties, such as for packing a column orbed. Insufficiently dense compositions may not settle properly or can beeasily disturbed by turbulence. Too dense compositions may not provide asufficient flow rate or be sufficiently porous. The density of thecomposition may be adjusted through various means, such as the ratio ofactive agent materials, the amount of support material, the supportmaterial composition, or the physical priorities, such as the mesh size,of the support material. In particular embodiments, the compositionshave a density of between about 0.5 g/cc and about 1.2 g/cc, such asabout 0.6 g/cc and about 1.0 g/cc.

Suitable compositions can be prepared by mixing a solution of the activeagent (or its precursors) with a base, such as sodium hydroxide, thusprecipitating a hydroxide, such as a hydroxide gel, of the active agent.The active agent solution is typically at a comparatively acidic pH,such as a pH of about 1.8. The basic solution typically has a pH ofabout 9 to about 11, such as a pH 10 solution of NaOH. The pH of thebasic solution can be selected, among other things, to control the rateof precipitation or the volume of the resulting solution. In someimplementations, the solution of active agent is added to the base, sothat the base is in excess.

Particular embodiments of the present disclosure provide resilient orleach-resistant compositions. In a particular example, the rate ofaddition of the active agent solution to the base, or the base to theactive agent solution, can be selected or controlled to influence theproperties of the resulting composition. In particular embodiments, thetemperature of the mixed solution is monitored and used to control thespeed of addition. For example, the rate of addition can be selected sothat the temperature of the mixed solution does not exceed 60° C., suchas not exceeding about 45° C. In particular examples, the solution isheld in the range of 35° C. to 45° C. In embodiments employing solutionsabove room temperature, the degree of heating of the solution can beused to control the rate of addition. For example, the temperaturechange can be limited to no more than 20 degrees (such as 20° C.), suchas being maintained at a temperature increase of about 10 to about 20degrees (such as about 10° C. to about 20° C.).

In particular methods, the active agent or basic solution includes aquantity of support material. Typically, to facilitate the addition, thesupport material is included in the solution to which the other solutionis added. In yet further methods of the present disclosure, an activeagent is formed, such as described above by precipitating the activeagent from a solution of the active agent (or its precursors) in theabsence of the support material. The solid active agent may then bemixed with the support material.

The mixture is typically agitated during addition and for a period oftime after addition is complete, such as about an additional 2 hours.Agitation may be accomplished using standard commercial mixingapparatus, which can be selected based on the amount of the disclosedcompositions being prepared. In at least certain embodiments, the mixeris a blade or paddle type mixer operating at about 200-500 rpm, such asabout 300 rpm.

In particular embodiments, the composition is ultrasonicated duringand/or after addition of the active agent and base solutions, or theaddition of the active agent material to the support material.Ultrasonication may be accomplished using standard bath or probe(immersion) ultrasonication devices, which typically operate at afrequency of 25 kHz to about 42 kHz. Sonication is typically appliedafter precipitation of the iron and lanthanum species is complete and istypically applied for a period of about 10 minutes to about 60 minutes,although longer periods can be used. Longer sonication periods aretypically used with higher frequency sonication. Visual inspection ofthe composition can be used, in at least certain embodiments, todetermine when the composition has been sufficiently sonicated, as thecomposition typically achieves a uniformly mixed appearance.Ultrasonication of the composition can result in improvedcharacteristics, such as composition resilience or leach-resistance.Stronger or more resilient material can make the compositions easier touse, such as by withstanding turbulence when a fluid is passed through abed of the composition.

The amount of active agent in the active agent solution, or the amountof active agent material added to the support material, can be selectedto provide a desired amount of active agent in the final composition.For example, in some instances the support material incorporates amaximum of about 30 wt % of the active agent with which it is mixed. Infurther examples, the support material incorporates at least about 1 wt% of the active agent, such as between about 2 wt % and about 10 wt %.The amount of active agent included in a composition with a supportmaterial can be selected to provide a desired operational life,including based on the solute concentration expected in a particularapplication, as well as the desired flow rate, contact time, and bedlength.

After the composition has been mixed and subjected to any desiredpost-mixing steps, including washing to remove salts, fine, or activeagent not-adhered to a support, or screening, it may be dried, such asfor storage or manipulation. Any remaining liquid from the mixingprocess is typically removed, such as by decantation, filtration, orsuction, and the cake of material dried. Drying is typically carried outsuch that the finial composition contains about 10 wt % to about 30 wt %water. Although higher and lower percentages can be used, higherpercentages of water may result in sticky compositions that aredifficult to manipulate.

Particular drying conditions may vary based on the volume and thicknessof material to be dried. In order to prevent damage to the material, andhelp provide even drying, the composition are dried, in some examples,at relatively low temperatures, such as less than about 200° C. In moreparticular examples, the compositions are dried between about 60° C. andabout 100° C. Drying times are typically between about 5 and about 36hours, such about 12 to about 20 hours. The material can be dried by anysuitable process, including by heating the mixture in an oven or passinga stream of heated air over the material.

The presently disclosed compositions may be used in a variety offiltration applications. More particularly, the disclosed compositionscan be used to remove unwanted species, from solution. The presentcompositions can be used to remove a number of species, includingarsenic, tungsten, fluoride, bicarbonate, phosphate, vanadium, andboron.

Use of Disclosed Adsorbents

Solutions containing arsenic ions are contacted with the filteringcomposition. The solution typically remains in contact with thefiltering compositions for a period of time sufficient to remove asolute, such as arsenic ions, to a desired concentration range. Inparticular examples, about 1 to about 10 minutes, such as about 1 toabout 5 minutes, is sufficient to remove arsenic to the desiredconcentration, such as below about 10 ppb, when the concentration ofarsenic in solution is between about 5 and about 100,000 ppb.

Disclosed processes can be used to remove more than 99% of arsenicspecies from aqueous solution. In more particular implementations,concentrations of less than 5 ppb arsenic are achievable. In particularimplementations, adjustment of the solution pH is not required prior topassage through the filtering composition. Particular disclosedadsorbents are effective over a wide pH range, such as from about 4.0 toabout 10.0, such as about 5.0 to about 9.5.

The water to be treated may come from any suitable sources. Particularsource waters include raw water, well water, drinking water (chlorinatedor not), and process water. In particular examples of such processes,the metal salt hydroxides include lanthanum or iron-lanthanum-magnesium,such as iron-lanthanum-magnesium having a weight ratio between about1:1:0.8 and about 1:4:0.2.

In particular disclosed methods, the adsorbents are stable or leachresistant after removing arsenic. In more particular methods, suchabsorbents pass both the California Wet Test and the ToxicityCharacteristics Leaching Procedure (TCLP). The filtering compositionsmay be wet screened and washed before loading into a column or bed.

EXAMPLE 1 Preparation of Filtering Compositions

Preparation of Lanthanum Hydroxide Media (DE-LaH)

The procedure for preparing this composition was similar to thepreparation of media “G” in U.S. Pat. No. 6,200,482 B1, Mar. 13, 2001.In the case of any discrepancy in procedure, the present disclosureshall control.

200 cc of 0.5 M LaCl₃ solution was added to 50 g diatomaceous earth (DE)and mixed for 60 minutes. The slurry was allowed to sit for 24 hours,after which the excess solution was decanted. The resulting material wassubmerged in de-ionized (D.I) water and stirred gently. 10 M NaOH wasadded dropwise until the pH of the slurry was 10.0. The material wasallowed to settle and was filtered. The collected material was washed toremove excess salt. The collected material was dried at differenttemperatures.

Preparation of De-Lanthanum-Iron Hydroxide Media (DE-LFH)

The procedure for preparing this composition was similar to thepreparation of media “G” in U.S. Pat. No. 6,200,482. In the case of anydiscrepancy in procedure, the present disclosure shall control. 200 ccof 0.5 M LaCl₃ and 0.5 M FeCl₃ cocktail solution, prepared by dissolvinglanthanum chloride or lanthanum carbonate in ferric chloride solution,was added to 50 g diatomaceous earth and mixed for 60 minutes. Theresulting slurry was allowed to sit for 24 hours, and the excesssolution was decanted. The material was submerged in de-ionized waterand stirred gently. Next, 10 M NaOH was added dropwise until the pH ofthe slurry was 10.0. The material was then allowed to settle andfiltered. The collected material was washed to remove excess salt andthen dried at different temperatures.

Preparation of Lanthanum Hydroxide Media (LaH)

Nanocrystals of lanthanum hydroxide adsorption media were prepared bydissolving lanthanum salts, such as lanthanum chloride, lanthanumacetate in water, lanthanum nitrate, or lanthanum carbonate, inhydrochloric acid, followed by precipitation with sodium hydroxide at pH10.0. The precipitate was filtered out and air was passed through it,then the material was allowed to sit for 24 hours. The material wasdried at different temperatures ranging from about 25° to about 350° C.The dried material was crushed and wet screened for the appropriatesize. The material was washed to remove any residual sodium chloridesalt. A scanning electron micrograph of a LaH oxy-hydroxide is shown inFIG. 1.

Preparation of Lanthanum-Iron-Magnesium Hydroxide Media (LFM)

Nanocrystals of lanthanum-iron-magnesium hydroxide composition wereprepared by dissolving lanthanum salts, such as lanthanum chloride,lanthanum acetate, lanthanum nitrate, or lanthanum carbonate, andmagnesium oxide in ferric chloride or ferric nitrate solution, thenco-precipitating the hydroxides with sodium hydroxide at pH 9.0.Magnesium oxide was added to raise the pH to 10.0. The precipitate wasfiltered out and air was passed through it, then the material wasallowed to sit for 24 hours. The material was dried at differenttemperatures ranging from 25° to 250° C. The dried material was crushedand wet screened for the appropriate size. The material was washed toremove any residual sodium chloride salt.

The filtration of the precipitates can be accomplished with a centrifugeor a press belt filter, but any suitable process known in the art can beused. A scanning electron micrograph of a LFM oxy-hydroxide is shown inFIG. 2.

The properties of certain adsorbents prepared as described in thepresent Example are summarized in Tables 1 and 2, below.

TABLE 1 Characteristics of DE-LF and DE-LaH Materials Bulk DensityParticle Size % Loading of Active Media (g/cc) (mesh) Reagent onto DEDE-LF 0.44 10-32 30 32-100 30 DE-LaH 0.45 10-32 30 32-100 30

TABLE 2 Characteristics of LFM and LaH Materials Media Particle Surface% Composition by Weight (drying Bulk Size Area (SEM) temperature)Density (mesh) (m²/g) La Fe Mg Cl O LFM 1.1  32-100 67.02 33.3 19 5.76.7 33 (200° C.) 100-270 78.6 27 20.2 5.8 3.8 40.5 LaH 1.3  32-100 68.7157.2 Nil Nil 8.9 30.5 (200° C.) 100-270 82.73 56.6 Nil Nil 8.1 33.5 LFMwith 1.0  32-100 105.6 20.0 16.0 4.1 3.0 46.0 air (60° C.) 100-270 123.515.0 14.0 3.0 1.0 50.5

EXAMPLE 2 Removal of Arsenic from Synthetic

Removal with DE-LaH:

200 cc of synthetic 150 ppb arsenic solution was added to variousamounts of the compositions of Example 1, prepared without passing airbut dried at different temperatures, and gently agitated for 4-5minutes. After 4-5 minutes, the arsenic solution was filtered and thefiltrate analyzed for arsenic concentration. The synthetic arsenicsolution was prepared by dissolving known amount of chemical gradeNa₂HAsO₄.7H₂O in de-ionized water.

According to the results shown in FIG. 3, the concentration of arsenicwas reduced to below the recommended MCL 10.00 ppb, when 1.0 gram of theadsorbent material air dried at room temperature was used. Drying theadsorbent material at higher temperatures reduces its efficiency toremove arsenic from solution. In addition, using less than 1.0 gram ofthe adsorbent material was not as effective in removing arsenic to below10.0 ppb.

Removal with DE-LF and DE-LaH

200 cc of synthetic 150 ppb arsenic solution was added to 1.0 g of thedifferent compositions dried at room temperature and gently agitated for3-4 minutes. The test was conducted with different sizes of the testmaterials. After 3-4 minutes, the arsenic solution was filtered and thefiltrate analyzed for arsenic concentration. The results of the analysisare given in Table 3 below.

TABLE 3 Removal of Arsenic with DE-LaH and De-LF Material Particle Size(mesh) pH of Solution Final As con. (ppb) DE-La 10-32 8.5 5 DE-La 32-1008.5 10 DE-La—Fe 10-32 8.3 10 DE-La—Fe 32-100 8.3 8

From the results in Table 3, diatomaceous earth with LaH or LFMmaterials are both capable of removing arsenic.

EXAMPLE 3 Rapid Small Scale Column Test (RSSCT) for Removing Arsenicfrom University of Nevada Reno Tap Water

Several RSSCT were performed with the different media described inExample 1. The arsenic contaminated water was prepared by dissolvingknown amounts of chemical grade Na₂HAsO₄.7H₂O in the tap water. The pHand Eh of the water was measured after the addition of the arsenic.

RSSCT with DE-LF

32-100 mesh DE-LF material dried at room temperature was studied runninga column in a down-flow mode. Samples of the treated water were takenregularly for arsenic analysis. The pH, Eh and the flowrate of thesample were recorded. The samples were acidified in 10% nitric acid. Asshown in FIG. 4, breakthrough at 10 ppb was reached at about 1100 bedvolumes.

TABLE 4 Test conditions of column: Media was loaded dry Flowrate: 28-35cc/min. System Pressure: Constant less than 5 psi Average Contact Time:6 min. Bed dimension: 1.5″ diameter by 10″ long Influent pH: 7.5 BedVolume: 100 cc Effluent pH: 7.6 Mesh Size of Media: 32-100 No pHadjustment No backwash for adsorptive media

RSSCT with LFM and LaH

Testing with 32-100 mesh LFM and LaH Materials dried at 200° C.

The columns were run in an up-flow mode. The media were backwashed once.Samples of the treated water were taken regularly for arsenic andlanthanum analysis. The pH, Eh and the flowrate of the sample wererecorded. The samples were acidified in 10% nitric acid.

TABLE 5 Test conditions of column: 32-100 mesh Media were loaded dryFlowrate: 20-40 cc/min. System Pressure: Constant less than 5 psiContact Time: 1-2 min. Bed dimension: 0.9″ diameter by 4″ long InfluentpH: 8.0 Bed Volume: 40 cc Effluent pH: 8.3 No pH adjustment Adsorptivemedia were backwashed

Results of the RSSCTs are illustrated in FIGS. 5 and 6, which indicatethat both adsorbent materials can remove and reduce arsenicconcentration to below 10 ppb in drinking water. LFM media passed over10,000, and LaH media about 9,000, bed volumes before breakthrough at 10ppb. The average contact time for both columns was 1 minute, 15 seconds.Both media continued to remove arsenic at 21,000 bed volumes, indicatingtheir potential capacities.

After 21,000 bed volumes both media were backwashed. The results of thesecond run show a drop in arsenic concentration in the effluent waterfor both media. The volume of water treated was over 10,000 and 12,000bed volumes for LFM and LaH compositions, respectively. The averagecontact time for both media was 2.0 minutes.

RSSCT with LFM and LaH Materials Dried at 200° C.

100-270 mesh LFM and LaH Materials dried at 200° C. were studied fortheir arsenic removal characteristics. The column was run in an up-flowmode. Samples of the treated water were taken regularly for arsenic andlanthanum analysis. The pH, Eh and the flowrates of the samples wererecorded. The samples were acidified in 10% nitric acid.

TABLE 6 Test conditions of columns: Media were loaded dry Flowrate:20-10 cc/min. System Pressure: Constant less than Average Contact Time:1.6 min. 5 psi Influent pH: 8.2 Bed dimension: 0.9″ diameter by 2″Effluent pH: 8.5 long No pH adjustment Bed Volume: 20 cc No backwash ofAdsorptive Media

Results of the RSSCTs are illustrated in FIGS. 7 and 8. Both mediapassed over 14,000 bed volumes without reaching 10 ppb. The RSSCTresults demonstrate that DE-LFM, LFM and La materials can effectivelyremove arsenic from drinking water to below 10 ppb. The pH and Eh of thetreated tap water ranged from 6.8 to 8.8 and 173.0 to 182.0 mV,respectively.

Leaching of Lanthanum Results

Test results of lanthanum concentration in the column effluent aredepicted in FIGS. 9-12. The results indicate lanthanum appears in waterat initial stages of treatment of the water regardless of the particlesize of the adsorbing composition. This could be attributed to very fineresidual lanthanum hydroxide particles that passed through the filters.The concentration of lanthanum reduces to less than 1.0 to about 1.5 ppbfrom 3500 to over 20,000 bed volumes of water passed.

EXAMPLE 4 Preparation of Adsorbent Compositions from Nitrate Salts

A variety of lanthanum-iron compositions were prepared from nitratesalts by various routes and subjected to various combinations of work upconditions. Lanthanum/iron filter composition A was prepared asdescribed in FIG. 13. Composition B was prepared similarly, except thatthe drying temperature was 100° C. and the moisture content of thecomposition was about 5-10%. A further composition C was prepared asdepicted in FIG. 14. Composition D was prepared in an analogous manner,except step 4 was omitted. Material E was prepared according to FIG. 14,except that step 7 was omitted. Instead, the washed material was keptmoist (no drying), with moisture content of about 20-40%.

Material F was prepared as shown in FIG. 15. Material G was preparedanalogously, with the exception that step 4 was omitted. Material H wasprepared as illustrated in FIG. 16. The properties of the variouscompositions are summarized in Table 7.

TABLE 7 Composition Characteristics Bulk Density Particle Surface MediaColor (g/cc) Size (mesh) Area (m²/g) Structure A Brown 1.0 −325 198.5Crystalline  20 × 200 236.7 Crystalline B Reddish 1.0 −325 171.6Crystalline Brown C Reddish 0.7 −325 197.8 Crystalline Brown D Reddish0.6 −325 218.5 Crystalline Brown E Reddish 0.7 −325 197.8 CrystallineBrown F Reddish 0.7 100 × 325 187.1 Crystalline Brown G Reddish 0.8 100× 325 188 Crystalline Brown H 1.0 −325 253 Crystalline

EXAMPLE 5 Simulated Rapid Small Scale Column Test (RSSCT) for ArsenicRemoval Using La—Fe Nitrate Compositions

The arsenic removing capabilities of the media described in Example 4were tested using groundwater obtained from Fernley, Nev., using theRSSCT procedure of Example 3. The empty bed contact time was threeseconds. The results of these tests are depicted in FIGS. 17 to 20. Asshown in the Figures, compositions A-H were effective in removingarsenic from the test solution.

EXAMPLE 6 Arsenic Stability

Characterization of Spent Media

Spent I, a lanthanum-iron-magnesium active agent on a diatomaceoussupport, was characterized for total arsenic and other contaminantsadsorbed, residual adsorptive capacity (RAC) for arsenic, surface area,TCLP and composition (XRD & SEM).

RAC Testing for Arsenic

“Spent” I, a lanthanum-iron active agent on a diatomaceous earthsubstrate prepared according to the methods of the present disclosure,was studied to determine if it had any further capacity to adsorbarsenic. Fresh I was used as a control.

Material tested included I from a top portion of a column (TC), unwashedI, I washed with de-ionized water at pH 4.2, and unused I (control).Water used for testing was de-ionized water from Clark Station Lab.Arsenite in the form of sodium arsenite was used as the arsenic source.The pH of the water was adjusted to 6.6 using HCl and NaOH. Bleach wasused for arsenite oxidation.

RAC testing proceeded as follows. Four liters of 1000 ppm arsenitesolution was prepared using de-ionized water. Four drops of bleach(commercial grade) were added to the solution. The pH of the resultingsolution was adjusted to 6.5. For each leaching bottle, 10.0 g of eachmedia was added to 500 ml of the arsenic solution. Each bottle wasagitated for 12 hours in a shaker. The media was then allowed to settleand was filtered. The acidified filtrates were analyzed for arsenic. Themedia were dried to remove excess moisture content and weighed to checkfor any loss of material.

Test & Analytic Results

Results of the RAC, surface area, and carbon content analysis arepresented in Table 8. The spent media was sent to an independent lab foranalysis, the results of which are presented in Table 9. The compositionalso removed significant amounts of Ba, Cr, V, Pb, and Zn.

TABLE 8 Removal of Arsenic with I. Initial arsenic con. = 1005 ppm FinalAs Con. RAC for Surface Area % Carbon Media (ppm) Arsenic (ppm) (m²/g)Content I (TC) 17.8 50K 131.7 2.51 I (CUW) 23.3 49.8k NA 2.95 I (CW)23.4 49.8k NA NA I (control) 0.016 Over 50K 203.8 0.95

TABLE 9 Composition of I with Contaminants Substance Concentration(mg/Kg) Source Arsenic 1400  From Fernley Water (FW) Barium 210 Calcium6600  From FW Chromium 100 Possibly from Media and FW Copper 1300  FromFW Iron   280K From Media Lead 410 From FW Manganese 740 Possibly fromMedia and FW Vanadium 520 From FW Zinc 380 From FW Lanthanum   280K FromMedia

Arsenic Stability

The spent media were subjected to TCLP and arsenic leaching in alkalinemedium. Desoprtion was carried out as follows. Two de-ionized waterswere prepared, one at pH 3.1 and one at pH 10.1. In leaching bottles,1.0 g of media was added to 500 ml of pH adjusted de-ionized water. Thebottles were agitated, with samples being removed after 15, 45, 60, and1320 minutes. The samples were filtered, acidified, and analyzed forarsenic.

After 22 hours some of the spent media broke down to very fineparticles. The filtrate from the pH 3.1 solution was clearer than thefiltrate from the pH 10.1 solution. The pH of leach solutions wasmeasured; the 3.1 solution increased to 6.3 after leaching and the pH ofthe pH 10.1 solution decreased to 9.3.

As shown in FIG. 21, there was a gradual release of arsenic at pH 10.1during 22 hours of agitation and very minimal release of arsenic at pH3.1. The adsorbed arsenic in I appears to be quite stable in acidic ascompared with alkaline medium. The breakdown of the media in thealkaline solution after 22 hours may have contributed to the release ofarsenic.

The results shown in FIG. 22 indicate that significant amount of ironleached out in alkaline medium. The observed high concentration of ironafter 22 hours in pH 10.1 solution could also be due to the breakdown ofthe media. In acidic medium iron is very stable.

The high and sharp decline of lanthanum at pH 3.1, depicted in FIG. 23,suggests possible dissolution or washing of residual lanthanum from thecomposition. The gradual increase in lanthanum concentration at pH 10.1could be attributed to breakdown of the media due to prolongedagitation.

To verify the increase in concentrations of arsenic, iron and lanthanumobserved at pH 10.1 due to attrition, the compositions were dried after22 hours and weighed. In pH 3.1 solution, there was a loss of 0.07 g,about 7% of the original weight. In pH 10.1 solution there was a loss ofabout 0.13 g, about 13% of the original weight.

Characterization of spent I media suggests that composition I still hadsignificant arsenic absorbing capacity even after removing about 50,000ppm arsenic. The gradual release of arsenic from the media in alkalinesolution (pH 9.3-10.1) could be primarily due to desorption of iron.Lanthanum release in acidic solution could be due to dissolution ofresidual fine lanthanum particles and in alkaline solutions attributedto possible breakdown of media.

EXAMPLE 7 Arsenic Stability and Characterization Spent Medias

This example illustrates the stability of I and a competing E33 media(an iron oxide/hydroxide material available from Bayer MaterialScienceof Pittsburgh, Pa.) loaded with arsenic as a function of pH and time.Testing was done in two phases which included adsorption and desorptionof arsenic from the media.

The water used for testing was de-ionized water from Clark Station Lab.Arsenate in the form of sodium arsenate was used. HCl and NaOH were usedfor pH adjustments. The selected pHs of water were 6.6 for adsorption,4.0 and 9.0 for desorption. The procedure for the adsorption step was asfollows.

A 1000 ppm arsenate solution was prepared in de-ionized water. The pH ofthe arsenate solution was adjusted to 6.6. 5.0 g of each composition wasadded to 500 ml of the arsenate solution in a leaching bottle. Thebottle was agitated for 16 hours in a shaker. The media was allowed tosettle and then was filtered. The filtrate was acidified for arsenicanalysis. The media was dried to remove excess moisture content and thenweighed to check for any losses.

Desorption studies were carried out by preparing two D.I waters at pHs4.0 and 9.0. 1.0 g of was added to 500 ml of de-ionized (pH adjusted) inleaching bottles. The bottles were agitated. Samples were obtained ofthe leached solution at 15, 30, 60, 240, 480 and 1500 minutes. Thesamples were filtered and acidified for arsenic analysis.

The zeta potential of I, Fe(OH)₃, and Fe₂O₃ was studied by measuring thezeta potential over a range of pHs from about pH 2 to about pH 12. Thezeta point of each composition was measured. The results of thesestudies are shown in FIG. 24.

Results

TABLE 10 Adsorption of Arsenic from de-ionized water at pH 6.6., initialAs concentration was 1100 ppm Final As Conc. As removed As adsorbedMedia Final Weight (g) (ppm) (ppm) (ppm) I 4.2 564 536 50.4K E33 2.4 880220 22K

The results of the adsorption testing indicate that I has about twicethe adsorptive capacity of E33 for arsenic removal in D.I water. I alsoappears to be stronger than E33 when subjected to abrasion. About 50% ofE33 broke down compared to 10% of I.

As shown in FIG. 24, composition I had a higher (more basic) zeta pointthan the commercially available FeO₃ or Fe(OH)₃. Correspondingly, fromthe results presented in FIG. 25, I appears to have better stability inarsenic retention than commercially available E33 in acidic water. Idesorbed less arsenic over time than E33 despite its higher loading ofarsenic. The gradual decline of arsenic release after 60 minutes from 1could be attributed to re-adsorption of arsenic by iron.

I desorbs less arsenic than E33, despite higher arsenic loading. Theresults of the stability testing of I indicate the media is better thanE33 in removing and retaining arsenic.

Characterization of Spent Media

Spent compositions (I, E33 and GFH (available from Siemens WaterTechnologies of Warrendale, Pa.) were characterized for total arsenicadsorbed, TCLP and surface area. The results of these characterizationsare presented in Tables 11 and 12. I loaded more arsenic than E33 andGFH.

TABLE 11 Arsenic loaded by Medias Arsenic TCLP for Surface Area MediaLoaded (ppm) Arsenic (ppm) (m2/g) I 940 <0.2 (passed) 178 E33 540 <0.1(passed) TDB GFH 210 TDB

TABLE 12 I Digest Results of other contaminants ContaminantConcentration (ppm) Barium 180 Cadmium <12 Chromium 29 Lead 350 Mercury0.084 Selenium <380 Silver <12

EXAMPLE 8 Removal of Arsenic from Fernley Water

This Example demonstrates removal of arsenic from the city of FernleyNev. well water (FW), the composition of which is summarized in Table13, with different compositions and measures the effect of influentwater pH on performance. The medias I (described in Example 7), La(OH)₃(prepared by neutralizing LaCl₃ with NaOH at pH>10.) and Fe(OH)₃ (EC33)were all prepared. The testing protocol used for removing arsenic wasSRSCCT (A jar test that simulates rapid small scale column testing). Theinitial pH of FW was 7.8, which was adjusted with HCl. 0.5 ml of eachmedia in 500 ml water was used to simulate 1,000 bed volumes per run.The contact time was 30 minutes per run, which was about 3.0 secondsempty bed contact time.

TABLE 13 Fernley Well 4 Water Quality Substance Concentration (ppm)Source Total Alkalinity 160 CaCO3 Bicarbonate 160 Carbonate <2 Chloride33 Fluoride <0.1 Sulfate 110 TDS 620 Total Phosphous 0.02 Antimony<0.0025 Arsenic 0.037 Barium 0.032 Calcium 48 Silica 52 Copper 0.006Iron 0.053 Magnesium 14 Manganese <0.002 Vanadium 0.021 Potassium 7.7Hardness 170Media Characterization Results:

TABLE 14 Characteristics of Medias @ particle size −325 mesh: Media SA(m2/g) Density Final (dry Wt. g) I 188.5 About 0.7 0.42 J 56.3 About 1.10.55 Fe(OH)₃ 114.2 About 1.2 0.6

As can be seen from Table 14, composition I had the highest surface areaand lowest density compared to the iron hydroxide and composition J(lanthanum hydroxide).

Results

FIG. 26 summarizes the results of RSCCT with filtering compositions. Asshown, I was more effective in arsenic removal than iron hydroxide orlanthanum hydroxide. The influent pH of FW was not adjusted. From theresults presented in FIG. 27, the efficiency of I in removing arsenicincreases as the pH of the influent water decreases.

The lanthanum based media I has a higher surface area and a lowerdensity than the hydroxides of its constituent elements and is moreeffective in removing arsenic from well water than La(OH)₃ or E33.

EXAMPLE 9 Arsenic Removal from City of Laytonville Calif. Well Water(LW)

This Example describes the removal efficiency of I with and without pHadjustment and compares the performance of composition I and E33 inremoving arsenic. This Example also measures the ability of compositionI to remove competing anions, such as phosphate, vanadium, andbicarbonate.

The testing protocol used for removing arsenic was SRSCCT (a jar testthat simulates rapid small scale column testing). Test conditionsinvolved an initial pH of LW of 7.65. The pH was adjusted to 6.4 byaddition of HCl. 0.25 ml of each media in 500 ml water was used tosimulate 2,000 bed volumes per run. The contact time was 30 minutes perrun, which was about 3.0 seconds empty bed contact time.

TABLE 15 Laytonville Well Water Quality Substance Concentration (ppm)Source Total Alkalinity 180 CaCO3 Bicarbonate 220 Carbonate <1.0Chloride 6.1 Fluoride <0.1 Sulfate 43 TDS 360 Total Phosphous 0.632Antimony <0.0025 Arsenic 0.006-0.018 Boron 0.22 Calcium 46 Silica 26Copper N/A Iron <0.01 Magnesium 26 Manganese <0.005 Vanadium 0.087Potassium 0.54

Adsorption Results

From the results presented in FIG. 29, the medias 10.0 ppb breakthroughpoints were about 13,000 bed volumes for 1 and 4,500 bed volumes forE33. The comparatively low breakthrough point of both medias wasattributed to the water pH and the presence of competing phosphate andvanadium anions.

In order to improve on the performance of the medias the pH of LW wasadjusted to 6.45 before treatment. The results of this testing ispresented in FIG. 30 and illustrate E33 breaking through at 46,000 bedvolumes, while I still had capacity to remove more arsenic. The observeddrops in effluent arsenic concentration are due to rest periods fromboth compositions. The final pH of effluent water after 46,000 bedvolumes was about 6.8 for both compositions.

The removal of other contaminants, were also investigated and theresults are presented in FIG. 31 and Table 16. As illustrated in FIG.31, composition I has a very high affinity for phosphate, more so thanarsenic or vanadium. Composition I, however, preferentially removedarsenic over vanadium in LW at pH 6.45.

The removal of bicarbonate was investigated at 1,000 bed volume run atLW pH 6.4 and 2 hours contact time. The results of this investigationare presented in Table 16.

TABLE 16 Removal of Bicarbonate. Initial Concentration = 190 ppm MediaFinal Con. (ppm) % Removal I 77 59.5 E33 130 31.6

Although both medias removed significant amount of bicarbonate,composition I outperformed E33 in removing arsenic from Laytonville wellwater at pH 7.6 and 6.45. Composition I was also a very adsorbent forphosphate, vanadium and bicarbonate. The presence of these competinganions in higher concentrations than arsenic does not impede the abilityof composition I to remove arsenic over 46,000 bed volumes.

EXAMPLE 10 Removal of Arsenic from City of Reno Nev. STIMGID Water

The objectives of this Example were to check the removal efficiency of Iwith and without pH adjustment, and to compare the performance ofcomposition I and GFH in removing arsenic from STIMGID well water (RSW)is one of EPA test sites in Nevada. GFH was selected for comparisonbecause it was the media selected after EPA performed an RSCCT. Thetesting protocol used for removing arsenic was SRSCCT (a jar test thatsimulate rapid small scale column testing).

Test Conditions

The initial pH of RSW was 7.4. The pH of RSW adjusted with HCl to6.0-6.6. 0.25 ml of each media in 500 ml water was used to simulate2,000 bed volumes per run. Contact time was 30 minutes per run, which isabout 3.0 sec empty bed contact time.

TABLE 17 Reno STIMGID Water Quality Sustabce Concentration (ppm) SourceTotal Alkalinity 80 CaCO3 Bicarbonate 98 Carbonate <1.0 Chloride 1.0Fluoride <0.1 Sulfate 6.7 TDS 190 Total Phosphous N/A Antimony 0.01Arsenic 0.045 Boron 0.31 Calcium 6.4 Silica 60 Copper N/A Iron 0.053Magnesium 2.1 Manganese <0.005 Vanadium <0.01 Potassium 4.7

Adsorption Results

From the results presented in FIG. 32, composition I was more effectivein arsenic removal at pH 6.5 than 7.4. Based on the pH resultscomposition I and GFH were tested on RSW at pH range of 6.0-6.6. Resultsof this testing are presented in FIG. 33, which indicates that both GFHand composition I broke through at about 25,000 bed volumes when theinfluent pH of RSW was 6.6. Reducing the pH of the influent water below6.6 resulted in further removal of arsenic with composition I to below10.0 ppb. GFH, on the other hand, did not accomplish arsenic removalwhen the pH was adjusted to below 6.6.

The observed drops in effluent arsenic concentration are due to restperiods from both compositions. Final pH of effluent water after 46,000bed volumes was about 6.6 for composition I, and about 6.7 for GFH.

EXAMPLE 11 Anion Removal

The presence of other anions in water could compete with anions ofarsenic for adsorptive sites of composition I. The objective of thisExample was to compare the preferential removal of some common competinganions.

Test Conditions

The anions selected were phosphate, fluoride, vanadium, sulfate, silica,and arsenate. De-ionized water at pHs 6.5 and 8.5 and equal molarconcentration of the anions were used for testing. The anions weretested independently.

Results

The results presented in FIGS. 34 and 35 indicate that composition Iremoves most of these competing anions. The composition is moreefficient in adsorbing these competing anions at pH 6.5 than 8.2.Composition I preferentially removes other anions in the followingorder: PO₄>F>As >V>SO₄>SiO₂ at pH 6.5; and PO₄>F>V>As>SO₄>SiO₂ at pH 8.5

It is to be understood that the above discussion provides a detaileddescription of various embodiments. The above descriptions will enablethose skilled in the art to make many departures from the particularexamples described above to provide apparatuses constructed inaccordance with the present disclosure. The embodiments areillustrative, and not intended to limit the scope of the presentdisclosure. The scope of the present disclosure is rather to bedetermined by the scope of the claims as issued and equivalents thereto.

We claim:
 1. A free flowing filtering composition comprising lanthanumand iron hydroxide, the filtering composition having a surface area ofat least about 175 m²/g, having a bulk density of between about 0.5 g/ccand about 1.2 g/cc, and having a zeta point of at least about pH 9.0. 2.The filtering composition of claim 1, further comprising magnesium. 3.The filtering composition of claim 1, wherein the filtering compositionhas a surface area of at least about 200 m²/g.
 4. The filteringcomposition of claim 1, wherein the filtering composition has a surfacearea of at least about 185 m²/g.
 5. The filtering composition of claim1, wherein the filtering composition has a moisture content betweenabout 10 wt % and about 40 wt %.
 6. The filtering composition of claim1, wherein the filtering composition has a bulk density of between about0.6 g/cc and about 1.0 g/cc.
 7. The filtering composition of claim 1,further comprising a diatomaceous earth support.
 8. A method of formingthe filtering composition of claim 1, comprising adding a solutioncomprising lanthanum and iron to a basic solution.
 9. A method offorming the filtering composition of claim 1, the method comprising:precipitating an active agent comprising lanthanum and iron from asolution to produce the filtering composition; and drying the filteringcomposition at temperature less than about 200° C. until the filteringcomposition has moisture content between about 10 wt % and about 30 wt%.
 10. The method of claim 9, further comprising ultrasonicating thefiltering composition before drying the filtering composition.
 11. Themethod of claim 10, wherein the filtering composition is ultrasonicatedfor between about 10 minutes and about 60 minutes.
 12. The filteringcomposition of claim 1, the filtering composition having beenmanufactured by a process comprising: dissolving lanthanum nitrate andiron nitrate in a solution; and drying the solution at a temperatureless than about 200° C. to yield precipitated lanthanum hydroxide andiron hydroxide.
 13. The filtering composition of claim 12, wherein theprocess further comprises: after dissolving, heating the solution;stirring the solution and adding sodium hydroxide to adjust pH of thesolution; and subjecting the solution to ultrasonic conditioning.
 14. Afree flowing filtering composition comprising lanthanum and ironhydroxide, the filtering composition having a surface area of at leastabout 175 m²/g, having a moisture content between about 10 wt % andabout 30 wt %, having a zeta point of at least about pH 9.0, and havinga bulk density of between about 0.6 g/cc and about 1.0 g/cc.
 15. Thefiltering composition of claim 14, further comprising magnesium.
 16. Thefiltering composition of claim 14, wherein the filtering composition hasa surface area of at least about 200 m²/g.
 17. The filtering compositionof claim 14, wherein the filtering composition has a surface area of atleast about 185 m²/g.
 18. The filtering composition of claim 14, furthercomprising a diatomaceous earth support.
 19. A free flowing filteringcomposition comprising lanthanum and iron hydroxide, the filteringcomposition having a surface area of at least about 175 m²/g, having azeta point of between about pH 9.0 and about pH 10.0, and having a bulkdensity of between about 0.6 g/cc and about 1.0 g/cc, the filteringcomposition having been manufactured by a process comprising: dissolvinglanthanum nitrate and iron nitrate in a solution; heating the solution;stirring the solution and adding sodium hydroxide to adjust pH of thesolution; subjecting the solution to ultrasonic conditioning; and dryingthe solution at a temperature less than about 200° C. to yieldprecipitated lanthanum hydroxide and iron hydroxide.
 20. The filteringcomposition of claim 19, wherein the filtering composition has a surfacearea of at least about 200 m²/g.
 21. The filtering composition of claim1, wherein the filtering composition has a zeta point of between aboutpH 9.0 and about pH 10.0.
 22. The filtering composition of claim 1,wherein the filtering composition has a zeta point of between about pH9.5 and about pH 9.8.
 23. The filtering composition of claim 1, furthercomprising a support, wherein the support is diatomaceous earth, perliteor cellulose.
 24. The filtering composition of claim 14, wherein thefiltering composition has a zeta point of between about pH 9.0 and aboutpH 10.0.
 25. The filtering composition of claim 14, wherein thefiltering composition has a zeta point of between about pH 9.5 and aboutpH 9.8.
 26. The filtering composition of claim 14, further comprising asupport, wherein the support is diatomaceous earth, perlite orcellulose.
 27. The filtering composition of claim 1, wherein thecomposition has a particle size of 20x200 mesh.
 28. The filteringcomposition of claim 1, wherein the composition has a particle size of100x325 mesh.
 29. The method of claim 13, wherein the solution is heatedto a temperature of between 35° C. and 45° C.
 30. The method of claim13, wherein the solution is heated to a temperature of up to about 60°C.
 31. The filtering composition of claim 14, wherein the compositionhas a particle size of 20x200 mesh.
 32. The filtering composition ofclaim 14, wherein the composition has a particle size of 100x325 mesh.33. The filtering composition of claim 19, wherein the composition has aparticle size of 20x200 mesh.
 34. The filtering composition of claim 19,wherein the composition has a particle size of 100x325 mesh.
 35. Thefiltering composition of claim 19, wherein the solution is heated to atemperature of between 35° C. and 45° C.
 36. The filtering compositionof claim 19, wherein the solution is heated to a temperature of up toabout 60° C.